A lion at the Bissell Lions of Lake Manyara exhibit at the John Ball Park Zoo.File photo, Rex Larsen | The Grand Rapids Press

Katy Muldoon writes in the Oregonian that the Oregon Zoo's Amur tiger, Nicole, died unexpectedly Monday.

Nicole and her brother Mikhail were born Oct. 31, 1998, at the John Ball Zoological Garden in Grand Rapids and moved to the Oregon Zoo on Sept. 12, 2000.

The female tiger was spotted by a zoo visitor having seizures at about noon, March 24, and died within minutes, the paper reports.

"Amur tigers are among Earth's most endangered big cats. Fewer than 500 are believed to remain in their home range in Russia's far east.

Because male Amur tigers are typically solitary animals, the zoo doesn't plan to bring in another as long as Mikhail is alive. "He's too old to move," Smith said, "and it would be too stressful on him to introduce another companion."